Where I am going, you cannot come because you have decided to remain in your sins. In his letter to the Romans, St. Paul concludes his treatise on sin by saying that the wages of sin is death (cf. Romans 6:23). Death becomes the logical end-result of sin because sin separates us from God who alone is the source/origin and sustainer of life. The implication, therefore, is that sin and life are mutually exclusive and cannot coexist in an individual. As the readings for today remind us, one of the many ways through which sin can enter into our lives is unbelief.  
In the First Reading from the book of Numbers, we are reminded of how, because of their failure to cultivate a trusting faith in the Lord, the children of Israel ended up inviting death into their camp. They failed to believe in God’s providence even after witnessing God’s salvific acts on their behalf ever since they departed the land of Egypt. Their journey through the desert was certainly not a comfortable or easy one by any means. Not only were they forced to adjust to a life “on the run,” but they also had to make do with the scarce resources that the desert provided. Fortunately for them, the Lord God was by their side to accompany and provide for them. The only thing that was required of them was to place their trust in God and to commit themselves to the Lord’s care. However, each time some challenge came their way, they appeared to suffer some kind of memory loss. For instead of trusting that the Lord who had seen them through past challenges will rise to the occasion and come to their aid, all they did was to complain against Moses and God. Such ungratefulness did not sit well with God who was in turn forced to “punish” them.  
In the Gospel Reading, we see Jesus making it clear to the Pharisees the fate that awaits those who refuse to believe in him and in his message. Jesus came from God as the light and bearer of the truth.  He has come into the world as the only way to the Father. He has come as the giver and restorer of eternal life. But despite all the mighty signs that he worked as he preached the good news, not everyone believed his message. Those who chose to reject him and his message rejected their only means of attaining fullness of life (eternal life). In rejecting Jesus, the author of life, they had unwittingly chosen death over life.
Jesus comes to us with the good news that the fullness of life which was lost due to sin has been made available to us once again. The only thing we have to do is to open ourselves to Jesus and to his message. But for that to happen, we must believe in him. We must believe that he has been sent by the Father and that his message is the good news that the world has been awaiting. Only by believing in him will we become recipients of the fullness of life which is God’s gift to us in Jesus Christ.